Usually efficiency for power converters is reported through measurements of typical operating points for input voltage Vin, output voltage Vout and output current Iout. For any static operating point this method is well suited to calculate the efficiency.
Unfortunately in real life operation the operating conditions vary significantly and in most of the cases are unpredictable. Therefore an easy calculation of the efficiency of a switched mode power management controller is not possible with a calculation assuming static behavior.
With the trend in today's power management controllers to incorporate telemetry functions an on-chip calculation of the real world efficiency is highly desirable.